1. Field of the Invention
The present invention is directed to a device for affixing an electrode cable to an apparatus for emitting electrical pulses, and in particular to an electrode cable for use in vivo with an implantable medical apparatus such as a pacemaker or a defibrillator, wherein the electrode cable is of the type having a pin-like proximal end and wherein the apparatus is of the type having a connector part, which contains the affixing device, for receiving and holding the pin-like proximal end of the electrode cable.
2. Description of the Prior Art
An affixing device of the type generally described above is disclosed in German OS 2 518 571. This device is for connecting at least one pacemaker electrode to a pacemaker. The affixing device includes a screw, disposed perpendicularly to the longitudinal axis of the electrode cable when the cable is contained in the connector, the screw being screwed into the connector part from the top side of the connector part to affix the electrode cable at a point on the distal end thereof. To prevent body fluids from penetrating into the connector part, the opening for the screw is provided with a sealing plug. By means of the use of a screw and a sealing plug, the connector part is relatively tall, which is undesirable in view of the goal of achieving a pacemaker having a smallest possible size. Moreover, this known affixing device presents problems for the implanting physician in securing the electrode cable to the pacemaker. To ensure that the screw which affixes the electrode cable has been sufficiently tightened, but without damaging the coupling site, tightening is performed with a special screwdriver which is designed to snap (break) or at least partially fracture, once the desired torque value has been achieved. The sealing plug is then applied by means of another special tool. This makes connecting the electrode cable to the pacemaker an relatively intricate procedure for the physician. Moreover, the affixing procedure occurs in conjunction with implantation of the electrode cable and the pacemaker. This means that the distal end of the electrode cable has already been introduced into the venous system of the patient, and placed, for example, in the heart just prior to the time that the electrode cable is to be connected to the pacemaker. Since the electrode cable has already been implanted, this limits the freedom of movement which is available to the physician for manipulating the electrode cable during the procedure for affixing the proximal end of the electrode cable to the pacemaker. Another disadvantage associated with this known device is that it is awkward to release the electrode cable from the pacemaker by reversing the affixing process, which may be necessary if the electrode cable is defective, or become defective over time, or if the pacemaker battery must be replaced. Separating the electrode cable from the pacemaker is not easy given this known affixing device.
A so-called "black hole"-type pacemaker coupling is described in U.S. Pat. No. 4,913,147. In this type of pacemaker coupling, the proximal end of the electrode cable is affixed to the pacemaker and seals the affixing area without the use of screws and sealing plugs. This is accomplished either using a spring, which is provided in the pacemaker connector socket and which can engage the pin-like proximal end of the electrode cable perpendicularly to the longitudinal axis of the pin, or using a ring attached to the pacemaker connector socket and through which the pin-like cable end is inserted. The ring alters its shape following insertion of the proximal cable end into the connector socket, so as to clamp and affix the proximal end of the cable in the connector socket. Both the spring and the ring are made of a metal alloy which has a shape at a first temperature which permits entry of the proximal end of the electrode cable into the pacemaker connector socket and which changes shape at a second temperature (body temperature in this instance) to affix the electrode cable end in the desired manner. A disadvantage of this known type of electrode affixing device is that the electrode cable cannot be reliably coupled to the pacemaker until the pacemaker and the electrode have been implanted, i.e., when the spring or the ring has reached the body temperature.
Another "black hole"-type pacemaker coupling is disclosed in European Application 0 048 760. In this known coupling, electrode connection is also achieved without the aid of screw fasteners or sealing plugs. This known pacemaker coupling includes a helical spring which is coaxially arranged on the proximal end of the electrode cable which is introduced into the connector socket. The helical spring extends along a part of the length of the cable socket. The proximal end of the electrode cable is clamped in the connector socket by flanges carried on sleeves which surround the helical spring when the proximal end is inserted into the connector part. The inner diameter of the helical spring is somewhat smaller than the outer diameter of the proximal end of the electrode cable which is to be connected to the pacemaker. When the electrode end is affixed, this end is introduced partially into the screw helical spring and is simultaneously rotated in a direction counter to the coil direction of the helical spring, so that the helical spring expands as the proximal end of the electrode cable is advanced into the connector socket. When the electrode end is completely inserted, the spring bias causes the helical spring to try to resume its original dimensions, thereby applying pressure to affix the proximal end of the electrode cable. The pacemaker connector socket also includes a connector part which is separate from the helical spring. This known pacemaker coupling thus has a relatively complicated structure and if the aforementioned rotation of the electrode end required for completing the coupling does not occur, the electrical contact surface on the electrode end, and even the helical spring in the pacemaker socket, may be destroyed.